Qualitative and quantitative change of the tolerance to liposomal amphotericin B triggered by biofilm maturation in C. parapsilosis

Candida parapsilosis is an emerging opportunistic pathogen present in both clinical and natural environment, with a strong frequency of biofilm forming strains. While the drugs active against biofilm are rare, liposomal amphotericin B is credited with an antibiofilm activity in some opportunistic species of the genus Candida. Using freshly isolated strains from hospital environment, in this paper we could show the prevalence of biofilm forming vs. nonbiofilm forming strains. The former displayed a large variability in terms of biofilm biomass and metabolic activity. Liposomal amphotericin B minimum inhibitory concentration (MIC) of planktonic cells was below the breakpoint, whereas the sessile cells MIC (SMIC) was 1 or 2 orders of magnitude above the planktonic MIC. When the drug was applied to freshly attached cells, that is, biofilm in formation, the MIC (called SDMIC) was even below the MIC value. All resistance metrics (MIC, SMIC, and SDMIC) were quite variable although no correlation could be detected between them and the metrics used to quantify biofilm activity and biomass production. These findings demonstrate that young biofilm cells are even more susceptible than planktonic cells and that early treatments with this drug can be beneficial in cases of prosthesis implantation or especially when there is the necessity of a CVC reimplantation during a sepsis.